Liquid crystal displays (LCDs) have been widely used as various displays because of their characteristics of low power consumption, excellent picture quality and light weight. For example, LCDs have been developed for computer monitors, televisions and mobile phones.
In the LCD manufacturing process, two glass substrates having a 10 μm gap between them are bonded to one another by a sealant. Then the liquid crystal is injected into the space between the two substrates. There are electrodes inside the two grass substrates. The electrodes are made of transparent conductive membranes and control the displays of characters and images. Applying controlling electrical signals to the membranes can control the displays of the characters and images.
During the manufacturing process of the LCDs, the sides where the two glass substrates are bonded will inevitably have small gaps with a few μm in the width. When injecting the liquid crystal material into the space between the two glass substrates, the liquid crystal material can invade the gaps by the capillary tube phenomenon. Since the contaminants in the atmosphere can dissolve in the crystal liquid material in the gaps and the gaps are very close to the positions where the controlling electrical signals are applied to the transparent electrodes, as a result, there can be insulation deterioration problems. Therefore, the crystal liquid material in the gaps needs to be cleaned.
Since the gaps are very narrow and are normally fewer than 10 um in width, the cleaning agents need to have highly effective cleaning capabilities in order to remove the liquid crystal material in the gaps. Among the most commonly used cleaning agents, organic solvents having halogen, such as fluohydrocarbon, 1,1,2-trichloroethane, 1,1,2-trichloroethene, perchloroethene and dichloromethane work relatively well. However, there are significant restrictions on the use of organic solvents having halogen since the restrictions on the use of the organic solvents are an important part in the world environmental protection policies.
With the demands for alternative cleaning agents, various new cleaning agents that can substitute said organic solvents having halogen have been developed, in particular, hydrocarbon solvents or mixed compound of both hydrocarbon solvent and polyglycol ether. For example, Patent JP10-25495 disclosed an effective cleaning agent for the LCDs. Said cleaning agent comprises of 5-95 wt % saturated hydrocarbon and/or saturated cycle having boiling points between 60° C. and 280° C. (For example, n-Decane or Cyclododecatriene-1,5,9), and 5-95 wt % ethylene glycol having the chemical formula of R1-(O—CnH2n)m—O—R2 (in particular, R1 and R2 are H, alkyl oracyl-, the total number of carbon atoms in R1 and R2 is 1 to 20, n is 2 or 3; m is an integer between 1 and 3). (For example, vinyl ethylene glycol dimethyl ether). However, said cleaning agent has relative weak cleaning capabilities and high flammability.
Moreover, in the manufacturing process of the LCDs, a mother glass is cut into small glass substrates and lots of powders are generated in the cutting process. These powders can attach to the surfaces of the electrode terminal so as to hamper the later sealing process. Moreover, the surface foreign contaminants such as glass powders normally attach to the surfaces of the LCDs by inter-molecular force. But they can also strongly attach to the surfaces of the LCDs using liquid crystal material as a binding agent. As a result, the cleaning agent needs to have much higher cleaning capabilities to remove the surface contaminants. For the most commonly used cleaning agents for the glass powders, the patents JP 5-271699, JP 7-305093 and JP 2001-181699 disclosed cleaning agents that are alkaline cleaning agents. However, the alkaline cleaning agents not only cause surfaces damages for the LCDs, but also cannot effectively remove the glass powder attached to the surfaces of the LCDs.
With the recent development in the high-density technology of the LCDs, the gap between the two glass substrates is getting narrower. Moreover, with the increasing demands for better throughput and higher passing rate for the production, the cleaning agents need to be able to clean the LCDs effectively in a very short time. The cleaning agents need effectively clean not only the liquid crystal material in the gaps near the bonding of the two glass substrates, but also the foreign contaminants on the surfaces of the electrode terminal. Furthermore, currently used STN liquid crystal material comprises of aromatics with —CN as typical substituents; while the TFT liquid crystal material comprises of aromatics with —CN as typical substituents. Since these two liquid crystal materials have substantial differences in the molecular structures and physical properties, there are demands for versatile LCD cleaning agent compounds suitable for diverse molecular structures and physical properties.
Due to the limitations of the prior art, it is therefore desirable to have novel LCD cleaning agents that can effectively remove not only the liquid crystal material in the gaps between the sides of the two glass substrates, but also the foreign contaminants attached to the surfaces of the LCDs.